This invention relates to rotary drill bits and more particularly relates to a novel and improved drill bit assembly which can be retrievably mounted at the lower end of a conventional drill string and has pivotal blade arms which can be expanded radially outwardly by fluid pressure combined with the rotational force of the drill string and the frictional force of the drill string weight on the material being bored.
Numerous types of retrievable drill bit assemblies have been devised for downhole or earth boring operations but in the past have been costly to manufacture and operate, time-consuming and not capable of performing different types of boring operations, such as, milling operations. Representative patents are U.S. Letters Patent Nos. 2,203,998 to D. J. O""Grady, 2,814,463 to A. W. Kammerer, Jr., 3,196,961 to A. W. Kammerer, 3,552,509 to C. C. Brown, 3,554,304 to H. D. Link et al, 3,656,564 to C. C. Brown, 3,684,041 to A. W. Kammerer et al and 5,271,472 to R. E. Leturno.
There is a continuing demand and need for drill bit assemblies which are highly versatile as well as efficient and durable in use and specifically are conformable for use as a drill bit tool, mill section tool or combinations thereof and can be utilized, with or without fluid assist, with retrievable or stationary bits, with or without jet kerf cutting, with or without a pilot nose, and with or without tungsten carbide buttons, cutting teeth, cutting rollers or polycrystalline diamond inserts. Most desirably, the drill bit assembly of the present invention incorporates a unique combination and arrangement of cutters and fluid passages along one or more blade arms of a drill bit assembly; and which is further characterized by being easily and quickly retrievable and replaceable.
It is therefore an object of the present invention to provide for a novel and improved drill bit assembly which is highly versatile and conformable for use in performing various earth boring operations.
It is another object of the present invention to provide for a novel and improved method and means for mounting a drill bit assembly or other tooling at the lower end of a conventional drill string or casing string to carry out various downhole operations.
It is a further object of the present invention to provide for a novel and improved method and means for mounting drill bits and other tools at the lower end of a conventional drill or casing string wherein the tools are quickly retrievable and replaceable.
It is a further object of the present invention to provide for a novel and improved drill bit assembly which employs a unique combination of cutting inserts and fluid passages to carry out downhole cutting operations; and specifically wherein the cutting elements may be employed alone or in combination with fluid pressure to perform different cutting and kerfing operations.
It is a still further object of the present invention to provide for a novel and improved drill bit assembly in which cutting inserts are immovably positioned along a leading edge of the blade arm forming a part of each drill bit; and in an alternate but preferred form to provide for a series of rotatable cutter disks spaced along an undersurface of each blade arm to carry out cutting operations.
The present invention resides in a drill bit assembly to be lowered on a drill or casing string into a subsurface formation in which a sub is connected to a lower end of the drill string, and a drill bit has a pair of blades arranged in juxtaposed relation to one another including pivotal ends mounted in the sub about a common pivot member and blade arms extending tangentially from the pivotal ends between a position extending substantially in an axial direction downwardly from the sub and a cutting position extending in opposed perpendicular directions with respect to the rotational axis of the drill string, and the blade arms have a series of cutting elements along one edge thereof.
In one preferred form, the cutting elements are inserted in recesses along the entire length of each blade arm and include an arcuate surface portion which protrudes from an undersurface of the blade arm. In addition, the cutting elements have flat surface portions substantially flush with the leading edge of the blade arm. In a second preferred form, the cutting elements are in the form of cutter disks which are journaled about individual roller shafts on the undersurface of each blade arm, the axis of rotation of each cutter disk being such that the disk rotates along a line which is tangential to the radius of curvature of the drill bit at that location.
In either preferred form, each of the blades has a fluid passage extending at least along the length of the blade arm and a plurality of fluid discharge bores communicating with the fluid passage for discharge of fluid under pressure from the passage in the form of high velocity streams cutting into the formation. Most desirably, the discharge means extend transversely of the passage through an undersurface of each blade and is defined by nozzles extending through the blade behind the cutting element. For most efficient cutting and removal of the formation being drilled, the nozzle locations are staggered with respect to the cutting element location so that the cutting elements break up the material between the kerf lines formed by the nozzles. For example, if the nozzles are disposed only along one of the blades and the cutting elements disposed only along the other of the blades, the cutting elements will break up that formation material between the kerf lines formed by the nozzles on the one blade. If the cutting elements are positioned on both blades, they are preferably staggered with respect to one another so as to engage different radial distances in the formation between the kerf lines, and correspondingly if the nozzles are positioned along both blades should be offset with respect to one another to form kerf lines at different radial distances and thereby achieve enhanced cutting action. The number and spacing of cutting elements and nozzles will of course vary with the hardness of material being drilled, hole size and velocity of the fluid discharged.
From the foregoing, the method of drilling into a subsurface formation comprises the steps of discharging a high velocity stream of fluid through a plurality of nozzles in at least one of a pair of rotating blades whereby a series of kerf lines are formed in concentric circles, and placing a series of cutting elements on at least one other of the blades to break up the formation material between the kerf lines formed by the jet streams through the nozzles. Whether the nozzles and cutting elements are positioned along one or both blades, most desirably the cutting elements are offset with respect to the path of the nozzles so as to break up the formation between the kerf lines formed by the nozzles. When rotating cutter disks are employed as the cutting elements, the disks are oriented to follow or track the kerf lines formed by the nozzles to assist in breaking up the rock or other material between the kerf lines.
As an added feature of the present invention, the pivot member for the blades is removably seated in the sub and lift plates extend upwardly from the sub having a latching device which is engageable by a retrieval bar so as to effect latching engagement between the retrieval bar and latching member for the purpose of lifting the drill bit out of the hole for replacement.
There has been outlined the salient features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. In this regard, the term xe2x80x9cdrill stringxe2x80x9d is employed herein to interchangeably refer to a rotating string of drill pipes or casings. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.